• Call for Social Sciences Papers
  • Science Sessions: The PNAS Podcast Program
May 17, 2011; 108 (20)

Cover image

Cover image expansion

Cover image: Pictured is a modern version of the Borromean rings, a topological arrangement of three interlocked symmetric rings that owes its name to the Borromeo family of Italy on whose coat of arms the rings appear. Although the three rings cannot be pulled apart, no two of them are linked—a fact that becomes apparent when one of the rings is hidden from view. Jim Conant, Rob Schneiderman, and Peter Teichner derived this particular realization of the link from their theory of Whitney towers, where it represents the Jacobi identity, or IHX-relation. See the article by Conant et al. on pages 8131–8138, which is part of the Special Feature on Low Dimensional Geometry and Topology. Image courtesy of Jim Conant, Rob Schneiderman, and Peter Teichner.

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